Well, after I made my post, I did some research to make sure I was making a valid argument about the repair difficulties. From what I read, it seems like the idea that disc brakes are hard to repair, is a bit of a stretch. I didn't find any disc brake repair kits, but looking at the parts, you might need to carry an extra rotor, some bleeding tools and fluid, and some pads. Those replacement parts, plus the added weight of a typical set of disc brakes, might turn some weight-conscious people away from disc brakes.

If the things stopped working for some reason, or you broke an essential part, you wouldn't be able to get a new set too easily. I guess that is the sticking point, along with weight. If you think you have a chance to totally wreck the brakes, then I'd go with another brake type.

Also consider the terrain of your ride. If there are a lot of hills, those downhills fully loaded with gear could require some strong disc brakes. The weather also plays a part. Wet and muddy weather is no problem for discs.